/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * libc/stdlib/lib_rand.c
 *
 *   Copyright (C) 2007, 2011 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/
/* First, second, and thired order congruential generators are supported */

#ifndef CONFIG_LIB_RAND_ORDER
#define CONFIG_LIB_RAND_ORDER 1
#endif

#if CONFIG_LIB_RAND_ORDER > 3
#undef CONFIG_LIB_RAND_ORDER
#define CONFIG_LIB_RAND_ORDER 3
#endif

/* Values needed by the random number generator */

#define RND1_CONSTK  470001
#define RND1_CONSTP  999563
#define RND2_CONSTK1 366528
#define RND2_CONSTK2 508531
#define RND2_CONSTP  998917
#define RND3_CONSTK1 360137
#define RND3_CONSTK2 519815
#define RND3_CONSTK3 616087
#define RND3_CONSTP  997783

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static unsigned int nrand(unsigned int nLimit);

/* First order congruential generators */

static inline unsigned long fgenerate1(void);
#if (CONFIG_LIB_RAND_ORDER == 1)
static double_t frand1(void);
#endif

/* Second order congruential generators */

#if (CONFIG_LIB_RAND_ORDER > 1)
static inline unsigned long fgenerate2(void);
#if (CONFIG_LIB_RAND_ORDER == 2)
static double_t frand2(void);
#endif

/* Third order congruential generators */

#if (CONFIG_LIB_RAND_ORDER > 2)
static inline unsigned long fgenerate3(void);
static double_t frand3(void);
#endif
#endif

/****************************************************************************
 * Private Data
 ****************************************************************************/

static unsigned long g_randint1;
#if (CONFIG_LIB_RAND_ORDER > 1)
static unsigned long g_randint2;
#if (CONFIG_LIB_RAND_ORDER > 2)
static unsigned long g_randint3;
#endif
#endif

/****************************************************************************
 * Private Functions
 ****************************************************************************/

static unsigned int nrand(unsigned int nLimit)
{
	unsigned long result;
	double_t ratio;

	/* Loop to be sure a legal random number is generated */

	do {
		/* Get a random integer in the requested range */

#if (CONFIG_LIB_RAND_ORDER == 1)
		ratio = frand1();
#elif (CONFIG_LIB_RAND_ORDER == 2)
		ratio = frand2();
#else							/* if (CONFIG_LIB_RAND_ORDER > 2) */
		ratio = frand3();
#endif

		/* Then, produce the return-able value */

		result = (unsigned long)(((double_t)nLimit) * ratio);
	} while (result >= (unsigned long)nLimit);

	return (unsigned int)result;
}

/* First order congruential generators */

static inline unsigned long fgenerate1(void)
{
	unsigned long randint;

	/* First order congruential generator.  One may be added to the result of the
	 * generated value to avoid the value zero.  This would be fatal for the
	 * first order random number generator.
	 */

	randint = (RND1_CONSTK * g_randint1) % RND1_CONSTP;
	g_randint1 = (randint == 0 ? 1 : randint);
	return randint;
}

#if (CONFIG_LIB_RAND_ORDER == 1)
static double_t frand1(void)
{
	/* First order congruential generator. */

	unsigned long randint = fgenerate1();

	/* Construct an floating point value in the range from 0.0 up to 1.0 */

	return ((double_t)randint) / ((double_t)RND1_CONSTP);
}
#endif

/* Second order congruential generators */

#if (CONFIG_LIB_RAND_ORDER > 1)
static inline unsigned long fgenerate2(void)
{
	unsigned long randint;

	/* Second order congruential generator. */

	randint = (RND2_CONSTK1 * g_randint1 + RND2_CONSTK2 * g_randint2) % RND2_CONSTP;

	g_randint2 = g_randint1;
	g_randint1 = randint;

	/* We cannot permit both values to become zero.  That would be fatal for the
	 * second order random number generator.
	 */

	if (g_randint2 == 0 && g_randint1 == 0) {
		g_randint2 = 1;
	}

	return randint;
}

#if (CONFIG_LIB_RAND_ORDER == 2)
static double_t frand2(void)
{
	/* Second order congruential generator */

	unsigned long randint = fgenerate2();

	/* Construct an floating point value in the range from 0.0 up to 1.0 */

	return ((double_t)randint) / ((double_t)RND2_CONSTP);
}
#endif

/* Third order congruential generators */

#if (CONFIG_LIB_RAND_ORDER > 2)
static inline unsigned long fgenerate3(void)
{
	unsigned long randint;

	/* Third order congruential generator. */

	randint = (RND3_CONSTK1 * g_randint1 + RND3_CONSTK2 * g_randint2 + RND3_CONSTK2 * g_randint3) % RND3_CONSTP;

	g_randint3 = g_randint2;
	g_randint2 = g_randint1;
	g_randint1 = randint;

	/* We cannot permit all three values to become zero.  That would be fatal for the
	 * third order random number generator.
	 */

	if (g_randint3 == 0 && g_randint2 == 0 && g_randint1 == 0) {
		g_randint3 = 1;
	}

	return randint;
}

static double_t frand3(void)
{
	/* Third order congruential generator */

	unsigned long randint = fgenerate3();

	/* Construct an floating point value in the range from 0.0 up to 1.0 */

	return ((double_t)randint) / ((double_t)RND3_CONSTP);
}
#endif
#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Function:  srand, rand
 ****************************************************************************/

void srand(unsigned int seed)
{
	g_randint1 = seed;
#if (CONFIG_LIB_RAND_ORDER > 1)
	g_randint2 = seed;
	(void)fgenerate1();
#if (CONFIG_LIB_RAND_ORDER > 2)
	g_randint3 = seed;
	(void)fgenerate2();
#endif
#endif
}

int rand(void)
{
	return (int)nrand(INT_MAX);
}

/****************************************************************************
 * Name:  random
 *
 * Description:
 *   Generate a non-negative, integer random number in the range of 0 through
 *   (LONG_MAX - 1)
 *
 ****************************************************************************/

long random(void)
{
	return (long)nrand(LONG_MAX);
}
